cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A174434 Numbers in A093891, but not A005153.

Original entry on oeis.org

10, 70, 350, 490, 572, 770, 836, 910, 1190, 1330, 1430, 1610, 1750, 1870, 2030, 2090, 2170, 2210, 2470, 2530, 2584, 2590, 2750, 2870, 2990, 3010, 3128, 3190, 3230, 3250, 3290, 3410, 3430, 3710, 3850, 3944, 4130, 4216, 4270, 4550, 4690, 5032, 5390, 5576
Offset: 1

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Author

T. D. Noe, Mar 19 2010

Keywords

Comments

A number n is in this sequence if the sums of distinct divisors of n form all the primes up to sigma(n), but do not form all the integers up to sigma(n).

Crossrefs

Programs

  • Mathematica
    Test[n_] := Module[{d=Divisors[n],t,lim,x}, t=CoefficientList[Product[1+x^i, {i,d}],x]; lim=PrimePi[Length[t]-1]; Count[t[[1+Prime[Range[lim]]]], _?(#>0&)] == lim && Count[t,0] > 0]; Select[Range[1000], Test]